Following the satisfactory definition of the immune competence of streptozotocin-induced diabetic rats, it is planned to evaluate the efficacy of immunosuppressive regimens in forestalling rejection of islets of Langerhans. Initially, rats will be made diabetic with intravenous streptozotocin. Lymphocytosis will be stimulated by injection of liver extract, and antilymphocyte globulin at the time of islet allografting will be attempted. In a separate protocol, induced diabetic rats will be allografted with islets and then given single, double, or triple immunosuppressive therapy with azathioprine, prednisone and cyclophosphamide.